Flexible coupling

ABSTRACT

A flexible coupling capable of transmitting moments and comprising a first member having a longitudinal axis ( 30 ) connected by at least three joints ( 27 ) to a second member ( 41 ) having a longitudinal axis substantially aligned with the longitudinal axis of the first member, the joints being circumferentially spaced apart about said axis, each joint comprising a first part ( 27 ) on one of the members and a second part ( 31 ) on the other member, the parts of each joint interfitting so that moments can be transmitted between said members by the joints and so that relative sliding and rotational movement can take place between the parts of teach joint, the joint parts on at least one of the members being flexibly arranged ( 41 ) so that the members may articulate relative to one another.

TECHNICAL FIELD

This invention relates to a flexible coupling. The invention isparticularly applicable to flexible couplings which include parts madeof plastic material, e.g. fibre reinforced epoxy, polyamide or otherresin.

BACKGROUND ART

Numerous types of flexible coupling are known for connecting two shaftsin driving engagement. In one type, there is a thin flexible disc towhich each shaft is joined by three, circumferentially-spaced, bolted orother rigid connections. Such connections impose strains on the disc inaddition to those required for torque transmission and articulation.These strains are associated with additional stresses which reduce thetorsional strength and fatigue life of the coupling.

It is an object of the present invention to provide a coupling in whichshafts, for example, may be joined to a flexible element by connectionswith additional degrees of freedom so that the stresses and strains onthe flexible element are reduced as compared with the above type ofcoupling and the life of the coupling thereby increased.

Another object is to increase, with respect to prior art couplings, themaximum articulation angle of the coupling as well as its maximumcontinuous running angle. A further object is to provide a coupling inwhich the stresses are reduced so that the coupling may include aflexible element made from a relatively low cost plastic material, suchas fibre-reinforced epoxy, polyamide or other resin, and which may bemanufactured easily, for example by injection-moulding.

The coupling of the invention may also be used as a static coupling forcorrecting two non-rotating parts so that moments may be transmittedacross the coupling.

DISCLOSURE OF INVENTION

According to one aspect of the invention we provide a flexible couplingcapable of transmitting moments and comprising a first member having alongitudinal axis connected by at least three joints to a second memberhaving a longitudinal axis substantially aligned with the longitudinalaxis of the first member, the joints being circumferentially spacedapart about said axes, each joint comprising a first part on one of themembers and a second part on the other member, the parts of each jointinterfitting so that moments can be transmitted between said members bythe joints and so that relative sliding and rotational movement can takeplace between the parts of each joint, the joint parts on at least oneof the members being flexibly arranged so that the members mayarticulate relative to one another.

According to a second aspect of the invention we provide a flexiblecoupling capable of transmitting torque and comprising a first memberhaving a rotary axis connected by at least three joints to a secondmember having a rotary axis, the joints being circumferentially spacedapart about said axes, each joint comprising a first part on one of themembers and a second part on the other member, the parts of each jointinterfitting so that torque can be transmitted between said members bythe joint and so that relative sliding and rotational movement can takeplace between the parts of each joint, the joint parts on at least oneof the members being flexibly arranged so that the members mayarticulate relative to one another.

According to a third aspect of the invention we provide a flexiblecoupling capable of transmitting torque from a first member having arotary axis via a second member to a third member having a rotary axis,the first member being connected to the second member and the secondmember being connected to the third member by joints, there being atleast three joints between the first and second members and between thesecond and third members respectively, the joints beingcircumferentially spaced about said axes, each joint comprising a firstpart on one of the members which is connected by the joint and a secondpart on the other connected member, the parts of each joint interfittingso that torque can be transmitted between said members by the joint andso that relative sliding and rotational movement can take place betweenthe parts of each joint, the joint parts on at least one of the membersbeing flexibly arranged so that the first and third members mayarticulate relative to one another.

Each joint may comprise a pin carried by one of the members and a socketcarried by the other member, the pin fitting into the socket so thattorque can be transmitted by the joint and so that relative sliding androtational movement can take place between each pin and the socket whichreceives it.

The joint parts may be mounted flexibly on only one member or may bemounted flexibly on more than one member.

The pins or sockets may be mounted on a ring and interconnected byflexible elements or the pins and/or sockets may be mounted on a rigidmember to which they are connected by flexible elements.

The longitudinal axes of the sockets and pins may be in a single planeor the axes of some of the sockets and pins may lie in one plane and thelongitudinal axes of the remaining sockets and pins lie in a secondplane parallel to the first plane.

The sockets and/or pins may be connected by flexible elements which arebowed in shape.

The sockets may be formed by inserts received in bores in a ring, thebores being flexibly interconnected. The pins may have part-sphericalheads received in cylindrical bores in the sockets or they may havecylindrical surfaces which are engaged with cylindrical bores in thesockets or inserts. The joints may be pin and socket joints with thepins detachably connected to the member on which they are carried.

The first member may comprise a wheel having internally projectingradial pins, the second member comprising a ring on which sockets aremounted, the sockets being inter-connected by flexible members, some ofthe sockets receiving the pins on the wheel and the third member havingoutwardly projecting pins which are received in the remainder of thesockets. The sockets may contain inserts in the form of bushes in whichthe pins are received. The inserts may be a snap-fit into the sockets.

The coupling may include a flexible annular disc having sockets securedthereto at positions spaced equi-angularly about the disc and twomembers each having a rotary axis and a plurality of outwardlyprojecting pins and wherein the pin's of each of the two members arereceived in alternate sockets on the disc. All the sockets may bearranged to project inwardly from the disc and the pins on the membersproject outwardly. Alternatively the sockets may project inwardly andoutwardly from the disc and each of said members may have radiallyinwardly and outwardly directed pins which are received in the inwardlyand outwardly directed sockets respectively.

The coupling may include sockets formed in or carried by a ring whichcomprises two parts which are detachably secured together, each saidring part providing a portion of each socket so that when the ring partsare secured together the socket portions are aligned to form thesockets, each ring part including flexible elements which inter-connectthe socket portions on the ring part. The ring parts may be identicaland may clip together. The ring parts may be prevented from becomingdetached from each other by inserts received in the sockets and whichreceive the pins.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a first embodiment of theinvention;

FIG. 2 is an exploded perspective view of a second embodiment of theinvention;

FIG. 3 is an exploded perspective view of a third embodiment of theinvention;

FIG. 4 is a perspective view of a form of torque transmitting memberwhich may be used in a coupling according to the invention;

FIGS. 5 and 6 are cross-sections through additional forms oftorque-transmitting members;

FIG. 7 is an exploded perspective view of a further embodiment of theinvention.

FIG. 8 is a partial exploded perspective view of a still furtherembodiment of the invention;

FIG. 9 is a diagram of another embodiment of the invention;

FIG. 10 is a diagram of another embodiment similar to FIG. 9;

FIG. 11 is a section through a further embodiment of the invention; and

FIG. 12 is an exploded perspective view showing the invention applied toa wheel;

FIG. 13 is an end view of the wheel of FIG. 12; and

FIG. 14 is a perspective view showing a coupling in which the ringcarrying the sockets comprises two detachable parts.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to FIG. 1, the coupling comprises a first member 10 havinga rotary axis 10 a and which includes an element 11 for receiving ortransmitting drive from or to the first member. The member carries threecylindrical sockets 12 each of which has a cylindrical bore 13. Thesockets 12 are connected to the element 11 by flexible elements 14 andby parts 15. Preferably the parts 11, 12, 14 and 15 are made as a singlemoulding of, for example, fibre-reinforced polyamide. The fibrereinforcement may be glass fibre. The member 10 may be joined to acompanion flange, not shown, by bolts 16. The longitudinal axes of thebores 13 lie in a single plane and the sockets 12 are equi-angularlyspaced about the rotary axis 10 a.

The coupling includes a second member 17 having a rotary axis 17 asubstantially aligned with the axis 10 a and which has a shaft 18 and atubular part 19. The second member can conveniently be made of metal,e.g. steel, and has three arms 20 projecting from the end thereof. Eacharm carries a trunnion 21, the trinnions being equi-angularly spacedabout the axis 17 a, and each trunnion has a reduced-section neckportion 22 and a head 23 which has a cylindrical surface 24,longitudinal axes of the surface 24 lying in a plane perpendicular tothe axis 17 a.

The coupling is assembled by inserting the heads 23 of the trunnions 21into the bores 13 of the sockets 12. The orientation and position of thesockets 12 is such that the relative movement of the first and secondmembers is constrained in directions parallel to the plane containingthe longitudinal axes of the bores 13. The heads 23 of the trunnions canslide and rotate in the bores 13 and this, and the flexibility of theelements 14, permits some articulation between the rotary axes 10 a and17 a of the first and second members 10 and 17 and allows a small amountof relative axial movement between the members 10 and 17. Each socket 12and trunnion 21 forms a joint to transmit torque between the first andsecond members, the joints being pin and socket joints. The trunnions 21may be detachably connected to the member 17 to ease assembly.

FIG. 1A shows an alternative type of trunnion 21 a having a partspherical surface 24 a. The centres of these surfaces for all thetrunnions lie in a plane perpendicular to the rotary axis 17 a.

Turning now to FIG. 2, the coupling comprises three members; the firstand third members are identical. The first member is indicated generallyat 25 and is identical in, construction to the second member 17 shown inFIG. 1 and will not be described further except to say that thetrunnions have heads 26 with circumferential cylindrical surfaces 27.The third member is shown at 25 a, is identical to the first member 25and has a rotary axis 25 b.

The second member 28 consists of six sockets 29 equi-angularly spacedaround the rotary axis 30 and each having a cylindrical bore 31. Thelongitudinal axes of the bores 31, which are indicated at 32, areequi-angularly spaced around the rotary axis 30 and all lie in a singleplane. The coupling is assembled by inserting the heads 27 of thetrunnions on the first member 25 into alternate ones of the bores 31 andinserting the heads of the trunnions of the third member 25 a into theremaining bores 31.

The heads of the trunnions can slide and rotate in the bores but theorientation and position of the bores is such that relative movement ofthe members to one another in the plane containing the longitudinal axisof the bores 31 is constrained.

The sockets 29 are interconnected by flexible elements 41 which arethinner in the middle than at the ends and which form a ring with thesockets 29 so that the second member 28 can be moulded as one piece. Theflexible elements 41 are parallel to and include the plane containingthe axes 32 of the bores 31. Articulation of the first and third membersis permitted by the flexibility of the elements 41 and the movement ofthe trunnion heads in the bores 31. Some relative axial movement is alsopermitted by the flexibility of the elements 41. As in FIG. 1, eachsocket 29 and trunnion forms a pin and socket joint connecting the firstmember to the second member or the second member to the third member.

The heads of the trunnions may be steel part-spherical elements insteadof steel cylinders such as indicated. The part-spherical shape would beused where the misalignment between the rotary axes 30 and 25 b of thefirst and third members is more than minimal and only a low torque hasto be transmitted because there would be a high contact pressure betweenthe spherical surface and the bores 31. The cylindrical heads 26 wouldbe used where there is a low angle of misalignment between said axes andhigh torque is to be transmitted since the contact pressures between thecylindrical surface and the bores would be less.

To aid assembly, the bores 31 may be fitted from the interior orexterior of the member 28 with plugs one of which is indicated at 35having a flange 36 at one end and a tubular portion 37 at the other. Thetubular portion 37 fits into the bore 31 and the head 26 of a trunnionwould fit into the bore 38 of the tubular portion. The plugs 35 may bemade of a wear-resistant or self-lubricating material. The trunnionscould also be detachable.

Referring now to FIG. 3, this shows a coupling which is similar to FIG.2 except that the sockets on the second member 42 are arranged on bothsides thereof. Thus there are three sockets 43 which are equi-angularlyspaced on one side and three sockets 44 which are equi-angularly spacedon the other side of the member. All the sockets are equi-angularlyspaced around the rotary axes of the coupling. The longitudinal axes ofthe bores in the sockets 43 lie in one plane perpendicular to the rotaryaxis of the member 42 and the longitudinal axes of the bores of thesockets 44 lie in a second and parallel plane. The sockets areinter-connected by flexible elements 45. The member 42 is preferablymoulded in one piece from fibre reinforced plastic, e.g.glass-reinforced polyamide. Such a coupling can accommodate, as well asangular misalignment, a small radial misalignment between the first andthird members 25 c and 25 d which have substantially aligned rotary axes25 e and 25 f respectively.

FIG. 4 shows the second member 46 for a coupling such as shown in FIG. 2or FIG. 3 of somewhat different shape. The member has six sockets 47each of which has a cylindrical bore 48. The longitudinal axes of thebores are indicated by the lines 49 all of which lie in the same plane.The flexible elements 50, 51 which join the sockets 47 are in thisinstance curved so that they lie alternately on different sides of theplane containing the longitudinal axes of the bores 48. Thus theflexible elements 50 lie on one side of the plane and the flexibleelements 51 lie on the other side of the plane.

The advantage of this construction is that it has increased torsionalcompliance and articulation capability. Also if there is a tendency forthe flexible elements 50 or 51 to buckle during operation they will notbuckle in a bi-stable way, i.e. they will not move from one side of theplane containing the longitudinal axes to the other during operation ofthe coupling.

Referring now to FIG. 5, this is a cross-section through another form ofsecond member of a coupling similar to that of FIG. 2 or FIG. 3 in whichthe sockets are arranged in parallel pairs. Thus there are sockets 52which have bores 53 with parallel longitudinal axes 54, there aresockets 55 which have bores 56 with parallel longitudinal axes 57 andthere are sockets 58 which have bores 59 with parallel longitudinal axes60. The sockets are inter-connected by flexible elements 61 in a mannersimilar to FIG. 3. The first and third coupling members will havetrunnion heads which engage in alternate sockets. Thus the trunnions 62a (shown in full lines) of the first member 62 engage in one each of thesockets 52, 55 and 58 and the trunnions 63 (shown in dotted lines) ofthe third member, not shown, engage in the other alternate sockets.

FIG. 6 shows an arrangement similar to FIG. 5 in which there are socketsin pairs with parallel axes. Thus there are sockets 70 having bores 71with parallel longitudinal axes 72; sockets 73 having bores 74 withparallel longitudinal axes 75 and sockets 76 having bores 77 withparallel longitudinal axes 78. The bores are shown containing the headsof the trunnions of the first and second members thus the heads of thetrunnions of the first member 81 are indicated in full lines at 79 andthose of the third member in dotted lines at 80.

Both in FIG. 5 and in FIG. 6 the trunnions are slidable and rotatable inthe bores of the sockets but the orientations and positions of the boresconstrain the first and third members in the plane containing thelongitudinal axes of the sockets. All the longitudinal axes of thesockets lie in a single plane. There are flexible elements 82interconnecting adjacent sockets as described in relation to FIG. 3.

Referring now to FIG. 7, this shows a three member coupling in whichthere is a first member 83, a second member 84 and a third member 85.The first and third members have substantially aligned rotary axes 83 aand 85 a respectively. The first member 83 is cylindrical and has threesockets formed in the circumference thereof, two of the sockets beingindicated at 86 and the sockets being equi-angularly spaced around therotary axis of the member 83. The second member, 84, is in the form of aone-piece moulding and comprises six pins interconnected by flexibleelements 87 in the form of a ring. Three of the pins 88 project inwardlyfrom the ring and three of the pins 89 project outwardly from the ring.

The third member 85 is a cylindrical member similar to the first member83 and is also provided with three sockets 90 equi-angularly spacedaround the member. The sockets 86 and 90 may have inserts 91 similar tothe inserts 35 described in relation to FIG. 2.

The pins 88 fit into the sockets 86 and the pins 89 fit into the sockets90. Thus the first member 83 is connected to the second member 84 by pinand socket joints allowing rotation and sliding between the parts ofeach joint and the second member 84 is connected to the third memberalso by similar pin and socket joints. Torque will be transmitted fromthe first member 83 to the third member 85 through these joints andarticulation between the first and third members 83 and 85 and someaxial movement will be permitted by the flexibility of the portions 87.

Referring now to FIG. 8, a conventional flexible disc is indicated at100. The disc comprises six fixing bosses, some of which are shown at101 interconnected by flexible leaves 102. One example of such acoupling is shown in DE-A-41 40 311. A three-armed spider is indicatedat 103 and on the arm 104 are secured two brackets 105 having circularapertures 106. Mounted on one of the bosses 101 is a pin 107. The pinhas a cylindrical outer surface 108 and a central slot 109. The boss 101is received in the slot 109. The pin 107 is held in position on the disc100 by a bolt 110 and a nut 111. The bolt is received in circular bores112 in the pin 107 which are provided on each side of the slot 109. Thebolt passes through the bores 112 and receives the nut 111.

When the coupling is assembled, the pin 107 is received in the apertures106 in the brackets 105. Thus a pin and socket connection is providedthe pin being provided by the pin 107 and the socket by the aperturedbrackets 105. The pin can slide radially and rotate within the apertures106. Although not shown, each arm of the spider 103 would have bracketssuch as 105 receiving pins such as 107 and there would be a secondspider which would receive similar apertured pins such as 113.

In practice, the coupling would be assembled by placing the disc withinthe brackets 105 in each spider and then assembling the pins from theinside by moving them radially outwardly into the apertures 106 and thensecuring the pins to the disc by the bolts and nuts 110 and 111.

Referring now to FIG. 9, this shows, in diagrammatic form anothercoupling. As in FIG. 8, there is a conventional flexible disc 114 havingsix, equi-angularly spaced bosses 115 interconnected by flexible leaves116. To each boss is connected a cylindrical socket such as 117, threeon one side of the disc and three on the other. Each socket has acylindrical bore 118 and a lug 119 at its radially outer end. The lug issecured to a boss 115 in a pivotal manner by means of a bolt assembly120. Each of the bosses of the coupling is provided with a socketsimilar to the socket 117 and these are indicated at 121, 122, 123, 124and 125. The sockets 117, 122 and 124 are on one side of the disc andreceive the arms 126, 127 and 128 respectively of a three-armed spider129. The arms 126, 127 and 128 are cylindrical and can slide and turn inthe bores 118 of the sockets. The similar arms of a second spider 130are received in the sockets 121, 123 and 125.

In every case the arms of the spiders are cylindrical and can slide andturn in the sockets and the sockets are flexibly interconnected by theleaves 116 of the composite disc.

FIG. 10 shows an arrangement similar to FIG. 9. Thus there is acomposite disc 131 having bosses such as 132 connected by flexibleleaves 133. Connected to each boss 132 is a socket one of which isindicated at 134. Each socket has two oppositely-facing bores 135 and136 and in each is received a pin 137 and 138 respectively. The pins 137and 138 are carried by an arm of a spider, the pins 137 being loopedover and connected to the pins 138. This looping over has been omittedfrom FIG. 10 for clarity.

There are six sockets such as 134, three of which are connected to thearms of one spider and three of which are connected to the arms of theother. Three of the sockets are on one side of the disc and three on theother. The pins connected to the spider arms can slide and rotate in thesockets and the sockets are flexibly interconnected by the leaves 133 ofthe composite disc.

Referring now to FIG. 11, there is shown a ring 140 made of compositematerial and this has six bores 141 equi-angularly spaced around theaxis of the ring. The bores are interconnected by flexible leaves 142.Two spiders 143 a and 143 b complete the coupling. The spider 143 a has,referring to FIG. 12, three pins 144 extending radially andequi-angularly spaced around the rotary axis 145. Each pin is receivedin the bore 156 of a socket 157 having flange 158 at its closed end. Thesocket is received in a bore 141.

Each pin can rotate and slide in its socket. There are three other pins149, 150 and 151 carried by the other spider 143 b which slide insockets similar to the socket 157 which are received in the bores 141.This arrangement makes for ease of assembly since the ring can beassembled to the two spiders and then the sockets assembled onto thepins of the spiders. The sockets 157 have projections 159 at their openends which snap under the inner end of the sockets 141 to hold thesockets 157 in place as shown in FIG. 11.

Referring now to FIGS. 12 and 13, a wheel, for example a road wheel of avehicle, is shown at 160. The wheel has a disc 161 which has a generallytriangular aperture 162. Projecting radially inwardly from each side ofthe aperture is a pin, two of which are shown at 163. A ring 164 similarto that shown in FIG. 2 is provided with six equi-angularly spacedsockets some of which are indicated at 165. A third member 166, whichcould be a drive shaft for the wheel, is provided with a cutaway tubularportion 167 which has three equi-angularly-spaced cylindrical trunnions,two of which are indicated at 168.

Three of the sockets 165 fit over the pins 163 and the other threesockets 165 receive the trunnions 168. Inserts such as 169 are insertedfrom the centre of the aperture 162 so as to receive the pins 163. Theinserts 169 are a snap fit in the sockets 165 as described in relationto FIG. 11.

Similarly, inserts 170 are inserted in a radially inward direction overthe pins 168 which are received in the other sockets in the ring 164,again the inserts 170 are a snap fit into the sockets. The inserts havebores such as 171 which receive the pins such as 163 or 168 and allowfor rotation and sliding of the pins in the bores.

FIG. 14 shows a coupling which is similar to that shown in FIG. 2 exceptthat the second member such as 28 in FIG. 2 is in this case made in twoidentical parts. Thus referring to FIG. 14 the member 172 provides sixsockets 173 equi-angularly spaced around the ring. The sockets receivethe pins 174 on a member 175 as described and the sockets also receiveinserts 10′ 176 which are snap fits in the sockets 173. The inserts 176have bores 177 in which the pins 174 are received so as to be able torotate and slide. A further member such as shown in FIG. 2 at 25 acompletes the coupling.

The ring 172 comprises two identical parts 178 and 179. Each partprovides half of each of the sockets 173, the halves being indicated at180 and 181 respectively. Each socket portion 180 181 is connected toits adjacent socket portion by a flexible web 182 183 respectively. Theportions 182 183 are provided with inter-fitting formations indicatedgenerally at 185 which snap together to hold the ring parts 178 179together. When the inserts 176 are inserted into the sockets 173 it willbe seen that the ring parts cannot become disengaged.

It will be seen that in each of the embodiments the first and secondmembers are connected by pin and socket joints which are equi-angularlyspaced around the rotary axes of the members. Where a third member isprovided as in FIGS. 2 to 14, the second member and the third member arealso connected by pin and socket joints. The flexibility of the couplingis provided in the arrangement of FIGS. 2 to 14 by flexiblyinterconnecting the sockets. In FIG. 1 the parts 14 provide a flexibleinterconnection of the sockets via the element 11.

In FIG. 1 the flexibility of the coupling is provided by the flexibleelements 14. However the trunnions 21 could be flexibly mounted on thesecond member 17 in place of, or in addition to, the flexible elements14.

In FIGS. 2 to 14 the flexibility of the coupling is provided by theflexible elements between the sockets. However trunnions such as 21 onthe first member and/or on the third member of each of these couplingscould be flexibly mounted on the member in place of or in addition tothe provisions of the flexible elements between the sockets.

In FIGS. 2 to 14 also, the sockets or pins on the second members of thecoupling could, instead of being inter-connected by flexible elements,be connected by flexible elements to a rigid ring or the like.

To ease assembly the trunnions in each of the embodiments may bedetachably secured to the members and secured to the members that carrythem after these have been located relative to the flexible ring.

As described the trunnions may be spherical or cylindrical and in mostcases the use of cylindrical trunnions is to be preferred so as to avoidtwisting of the sockets during the transmission of torque.

It will also be understood that although the device of the presentinvention has been described in terms of a rotating coupling, it couldbe used as a static coupling for flexibly connecting two non-rotatingparts in such a way as to enable moments to be transmitted therebetween.

1.-26. (canceled)
 27. A flexible coupling capable of transmitting torqueand comprising: a first member having a first rotary axis; a secondmember having a second rotary axis; and at least three joints connectingthe first and second members, the joints being circumferentially spacedabout said first and second axes, wherein each joint comprises a pincarried by the first member and a socket carried by the second member,the pin registering into the socket so that torque can be transmittedbetween said first and second members and so that relative sliding androtational movement can take place between each pin and associatedsocket, wherein each socket is connected by a flexible extension to thesecond member such that the first and second members can articulaterelative to one another.
 28. A flexible coupling according to claim 27wherein the pins have cylindrical surfaces which engage with cylindricalbores on the sockets.
 29. A flexible coupling according to claim 27wherein the pins have part-spherical heads received in cylindrical boresin the sockets.
 30. A flexible coupling according to claim 27 whereinthe pins are flexibly connected to the first member.
 31. A flexiblecoupling according to claim 27 wherein longitudinal axes formed by thesocket and pin joints lie in a first plane.
 32. A flexible couplingaccording to claim 31 wherein a longitudinal axis of at least one socketand pin joint lies in a plane parallel to the first plane.
 33. Aflexible coupling capable of transmitting torque and comprising: a firstmember having a rotary axis and comprising at least three pins; a secondmember comprising at least six sockets; and a third member having arotary axis and comprising at least three pins, wherein the first memberis connected to the second member by at least three joints and thesecond member is connected to the third member by at least three joints,the joints being circumferentially spaced about said axes, wherein eachjoint comprises a pin carried by the first or third member and a socketcarried by the second member, the pin registering into the socket sothat torque can be transmitted between the respective joint members andso that relative sliding and rotational movement can take place betweeneach pin and associated socket, wherein the sockets of the second memberare connected by flexible extensions such that the first and thirdmembers can articulate relative to one another.
 34. A flexible couplingaccording to claim 33 wherein the pins of at least the first or thirdmember are flexibly mounted thereto.
 35. A flexible coupling accordingto claim 33 wherein the sockets are mounted on a ring and interconnectedby flexible elements.
 36. A flexible coupling according to claim 33wherein longitudinal axes formed by the socket and pin joints lie in asingle plane.
 37. A flexible coupling according to claim 36 wherein atleast one longitudinal axis formed by a socket and pin joint lies in aplane parallel to said single plane.
 38. A flexible coupling accordingto claim 35 wherein the sockets are connected by flexible elements whichare bowed in shape.
 39. A flexible coupling according to claim 35wherein the sockets are formed by inserts received in bores in saidring, the bores being flexibly interconnected.
 40. A flexible couplingaccording to claim 33 wherein the pins have cylindrical surfaces whichengage with cylindrical bores on the sockets.
 41. A flexible couplingaccording to claim 33 wherein the pins have part-spherical headsreceived in cylindrical bores in the sockets.
 42. A flexible couplingaccording to claim 35 wherein the first member comprises a wheel havinginternally projecting radial pins.
 43. A flexible coupling according toclaim 42 wherein the sockets include inserts in the form of bushes inwhich the pins are received.
 44. A flexible coupling according to claim43 wherein the inserts are snap-fit into the sockets.
 45. A flexiblecoupling according to claim 35 wherein the first and third memberscomprise outwardly projecting pins received in alternate sockets on thering.
 46. A flexible coupling according to claim 45 wherein all thesockets are arranged to project inwardly from the ring.
 47. A flexiblecoupling according to claim 35 wherein the sockets alternatingly projectinwardly and outwardly, and wherein one of the first or third membershas inwardly projecting pins and the other of the first or third memberhas outwardly projecting pins, the pins being received in inwardly andoutwardly directed sockets, respectively.
 48. A flexible couplingaccording to claim 35 wherein said ring comprises two parts which aredetachably secured together, each said ring part proving a portion ofeach socket such that when the ring parts are secured together, thesocket portions are aligned to the form the sockets.
 49. A flexiblecoupling according to claim 48 wherein the ring parts are identical. 50.A flexible coupling according to claim 48 wherein the ring parts areprevented from becoming detached from each other by inserts received inthe sockets and which receive the pins.
 51. A flexible coupling capableof transmitting torque and comprising: a first member having a rotaryaxis and comprising at least three sockets; a second member comprisingat least six pins; and a third member having a rotary axis andcomprising at least three sockets, wherein the first member is connectedto the second member by at least three joints and the second member isconnected to the third member by at least three joints, the joints beingcircumferentially spaced about said axes, wherein each joint comprises asocket carried by the first or third member and a pin carried by thesecond member, the pin registering into the socket so that torque can betransmitted between the respective joint members and so that relativesliding and rotational movement can take place between each pin andassociated socket, wherein the pins of the second member areinterconnected by flexible elements such that the first and thirdmembers can articulate relative to one another.
 52. A flexible couplingaccording to claim 51 wherein the sockets of at least the first or thirdmember are flexibly mounted thereto.
 53. A flexible coupling accordingto claim 51 wherein the pins are mounted on a ring and interconnected byflexible elements.
 54. A flexible coupling according to claim 51 whereinlongitudinal axes formed by the socket and pin joints lie in a singleplane.
 55. A flexible coupling according to claim 51 whereinlongitudinal axes formed by the socket and pin joints lie in at leasttwo parallel planes.
 56. A flexible coupling according to claim 53wherein the pins are connected by flexible elements which are bowed inshape.
 57. A flexible coupling according to claim 53 wherein the pinsare detachably connected to the ring.
 58. A flexible coupling accordingto claim 51 wherein the pins have cylindrical surfaces which engage withcylindrical bores on the sockets.
 59. A flexible coupling according toclaim 51 wherein the pins have part-spherical heads received incylindrical bores in the sockets.
 60. A flexible coupling according toclaim 51 wherein the sockets include inserts in the form of bushes inwhich the pins are received.
 61. A flexible coupling according to claim51 wherein all the pins project outwardly.
 62. A flexible couplingaccording to claim 53 wherein the pins alternatingly project inwardlyand outwardly, and wherein one of the first or third members hasinwardly projecting sockets and the other of the first or third memberhas outwardly projecting sockets, the pins received in inwardly andoutwardly directed sockets, respectively.